RF power amplifiers are used in applications such as wireless cellular handsets. Wireless cellular devices may implement technologies that typically need particular power consumption requirements. In certain applications, power amplifiers implement or utilize analog signals, and specifically analog input signals that resemble sinusoidal waveforms, and typically use active devices as voltage-controlled current sources. Such power amplifiers and may be termed analog power amplifiers and typically belong to operational classes A, AB, B and C as known in the industry. Power amplifiers that implement digital signals or utilize digital or square input signals that resemble clock waveforms are termed digital power amplifiers and typically belong to operational classes D, E and F as known in the industry. Such power amplifiers typically use active devices as resistive switches. For analog power amplifiers, the main transistor acts as a rather linear element, whereas in for digital power amplifiers, the main transistor acts as a rather switch. Both analog and digital power amplifiers present common and unique issues. Common design issues include modulation fidelity, power switching, power control, and leakage as well as thermal gradients.
In certain design considerations, it is desirable to implement a digital power amplifier, also termed as power stage or RF digital to analog converter or DAC, instead of an analog power amplifier, such as when digital control is desired (i.e., having a digital clock signal); however, in applications such when lowering sensitivity for antenna reflections, typical implementation may be with an analog power amplifier that does not provide for a digital signal. Other design consideration may include proper power shutdown of arrays of power amplifiers. It is also desirable to have a high output power and highly efficient power amplifier.